The co-founder of a group supporting an Army private accused of leaking classified information to WikiLeaks filed a federal lawsuit today accusing the Department of Homeland Security of violating his civil rights by seizing his laptop without a warrant when he passed through security at O’Hare International Airport in Chicago.

David House, 24, a former MIT researcher from Cambridge, alleges in the suit filed in US District Court in Boston that federal agents seized his laptop, USB storage device, video camera, and cellphone when he arrived at the airport on Nov. 3 after a vacation in Mexico, then kept him from catching a connecting flight to Boston while they interrogated him about his association with Private First Class Bradley Manning.

The suit, filed on House’s behalf by the American Civil Liberties Union, says House “was asked no questions relating to border control, customs, trade, immigration, or terrorism,” yet agents kept his laptop, USB device, and camera for 49 days while they reviewed personal and private information as part of an investigation into his work for the Bradley Manning Support Network. The electronics were returned to him Dec. 22, a day after the ACLU faxed a letter to government officials demanding their immediate return.

“If the government had legitimate reason for wanting to seize my laptop … they could obtain a warrant,” House said during a telephone interview. “Instead they wait for me to cross the border so they can claim this nebulous authority.”